[Eeglablist] EEG Alpha Asymmetry

[Palaniappan, Ramaswamy]

Dear all,

Yes, the hemispheric index is one possible choice, where R would be a channel in the right hemisphere and L would be a channel in the left hemisphere.

Some simple possibilities in MATLAB: (var(x)-var(y))/(var(x)+var(y)) or (log(var(x))-log(var(y)))/(log(var(x))+log(var(y))) where x and y are EEG data from each hemisphere. I think for the latter case, the base for the log is immaterial if used in this manner.

I have used it successfully for analysing several bands for BCI design: R. Palaniappan, "Utilizing gamma band spectral power to improve mental task based brain computer interface design," IEEE Transactions of Neural Systems and Rehabilitation Engineering, pp. 299-303, vol. 14, no. 3, 2006.  

Best wishes,
Palani


-----Original Message-----
From: eeglablist-bounces at sccn.ucsd.edu [mailto:eeglablist-bounces at sccn.ucsd.edu] On Behalf Of Laszlo Balazs
Sent: 08 August 2007 15:29
To: eeglablist at sccn.ucsd.edu
Subject: Re: [Eeglablist] EEG Alpha Asymmetry

Dear Gregor and Arno,

I think log transformed power behaves more disciplined in terms of 
statistics.  Some people also prefer the hemispheric index (R-L)/(R+L) - 
again from log power - for it is independent of absolute power values 
that could be largely different between subjects. I am not familiar with 
the current trends though since I have long departed from the laterality 
business.
Best regards,
Laszlo

Arnaud Delorme wrote:
> Dear Gregor,
>
> first you need to compute alpha power. To do so may use the function 
> spectopo or newtimef to compute the alpha power. For example for a 
> single channel on the left and on the right.
>
> x = 10; % example of channel index on the left
> y = 11; % example of channel index on the right
> [ spec_x freqs ] = spectopo(EEG.data(x,:), EEG.pnts, EEG.frames, 'plot', 
> 'off');
> [ spec_y freqs ] = spectopo(EEG.data(y,:), EEG.pnts, EEG.frames, 'plot', 
> 'off');
> [tmp alpha_ind] = min( abs(freqs-10)); % find closest frequency to alpha 
> at 10 Hz
> asymmetry = spec_x(alpha_ind) - spec_y(alpha_ind) % I think asymmetryis 
> about subtracting power but I might be wrong.
>
> Hope this helps.
> Best regards,
>
> Arno
>
> gkohls at ukaachen.de wrote:
>   
>> Dear all,
>>
>> I collected resting EEG to analyze frontal Alpha asymmetry. Can anyone 
>> help me how to analyze alpha band and asymmetries with EEGlab? I tried 
>> but did not succeed.
>>
>> Many thanks in advance,
>> Gregor
>>     
>
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-- 

----------------------------------------------------------------------------
    Laszlo Balazs, Ph.D.          /      dr. Balázs László
Institute for Psychology HAS       /   MTA Pszichol¢giai Kutatóitézet
Budapest, P O B 398, H-1394 Hungary / Tel:+36(1)354-2410  Fax:+36(1)354-2416
                       www.cogpsyphy.hu/balazs





-- 

----------------------------------------------------------------------------
     Laszlo Balazs, Ph.D.          /      dr. Balázs László
Institute for Psychology HAS       /   MTA Pszichol¢giai Kutatóitézet
Budapest, P O B 398, H-1394 Hungary / Tel:+36(1)354-2410  Fax:+36(1)354-2416
                        www.cogpsyphy.hu/balazs



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